The present invention relates to a method for making various covers to be used in connection with an engine, and more specifically to a method for making such covers which are mainly made of a fibrous material having a good damping capacity.
Various covers are used for internal combustion engines. For example, there are rocker covers (cylinder head covers), front covers, dust covers, undercovers, engine air filter casings and their covers, noise reducing covers located in the vicinity of an engine, oil pans and hood insulators. These covers must be water-proof, oil-proof, light in weight, hard to some extent, and shape-retentive to some extent.
These covers are usually made of sheet metal, plastic or other hard material. Covers made of such a hard material are easily excited by the vibrations of an engine, and they tend to become a secondary source of noises which increases the engine noise.
Recently, there have been proposed covers which are made of a fibrous material having an excellent capability in absorbing sound and mechanical vibration. For example, Japanese Patent provisional publication Sho 54-80387 discloses such covers. Covers of this kind are made by mixing a synthetic resin and its cross linking agent to a fibrous material, and pressing the resultant mixture into a desired shape and a densely compressed state by the application of heat and pressure.
In order to make such covers impervious to rain water and engine lubricating oil, it is necessary to cover one or both of the surfaces of the fibrous material layer with a rubber layer having a water-proofness and an oil-proofness, because the layer of the fibrous material is not impervious in itself. It is, however, desirable to make the rubber layer as thin as possible because the rubber layer increases the weight of a cover, and raises the cost of material.